1. Field of the Invention
The present invention relates to a quality evaluation apparatus, a quality evaluation method, and an evaluation substrate that evaluates the quality of a multilayer capacitor.
2. Description of the Related Art
Chip components, particularly monolithic ceramic capacitors have been widely used in mobile terminals such as cellular phones and various electronic apparatuses such as personal computers. A monolithic ceramic capacitor includes a substantially rectangular component body including inner electrodes and dielectric ceramics that are alternately stacked on top of one another and outer electrodes formed on opposing end portions of the component body.
A monolithic ceramic capacitor is electrically and physically connected to a circuit board of an electronic apparatus by directly placing the outer electrodes onto mounting lands of the circuit board and bonding each of the mounting lands and the corresponding outer electrode using a bonding agent such as solder.
When an alternating-current voltage or a direct-current voltage on which an alternating current component is superimposed is applied to such a monolithic ceramic capacitor, mechanical deformation vibration is generated due to the piezoelectric and electrostrictive effects of a dielectric ceramic. The vibration of the monolithic ceramic capacitor is transferred to the circuit board, and the circuit board vibrates. When the circuit board vibrates, vibration sound audible to the human ear may sometimes be generated.
In order to solve the above problem, various configurations have been considered. For example, Japanese Unexamined Patent Application Publication No. 8-55752 describes a method of mounting a monolithic ceramic capacitor onto a substrate such that surfaces of inner electrodes are perpendicular to a surface of the substrate. Japanese Unexamined Patent Application Publication No. 2012-94784 describes that end surfaces of outer electrodes of a monolithic ceramic capacitor are clamped between connection terminals, and that the monolithic ceramic capacitor is mounted on a circuit board via the outer electrodes. Japanese Unexamined Patent Application Publication No. 2004-134430 describes that a monolithic ceramic capacitor is indirectly mounted on a circuit board via an interposer that is made of an insulating board.
Although various means for suppressing occurrences of vibration sound such as those described in Japanese Unexamined Patent Application Publication No. 8-55752, Japanese Unexamined Patent Application Publication No. 2012-94784, and Japanese Unexamined Patent Application Publication No. 2004-134430, which have been described above, have been proposed, there is no method of precisely measuring vibration sound and no method of comparing vibration sounds. Vibration sound changes depending on the frequency of a voltage that is applied to a multilayer capacitor. For example, in a method of measuring vibration sound that is disclosed in Japanese Unexamined Patent Application Publication No. 2012-94784, changes in vibration sound due to variation in frequency are complicated. In addition, the vibration sound changes in a more complicated manner depending on variations in a mounting state of a multilayer capacitor. When such complicated changes in vibration sound occur, it becomes difficult to compare vibration sounds of various multilayer capacitors. Therefore, there is a need for a method of precisely measuring vibration sounds of a substrate on which a multilayer capacitor is mounted.